The present invention relates to a decarbonylation process. More particularly, the invention relates to a selective decarbonylation process employing a palladium catalyst.
Para-t-butyl phenylpropionaldehyde and para-t-butyl-alphamethyl-phenylpropionaldehyde are widely used fragrance materials. Moreover, recently these materials have been suggested for use as fungicides. These compounds are currently prepared from para-t-butyl benzaldehyde or acrolein diacetates. The para-t-butyl benzaldehyde is prepared by a stoichiometric manganese oxidation. This oxidation, however, generates large quantities of solid waste which can present environmental problems. The acrolein diacetates on the other hand are difficult to handle and prepare and such method is a relatively inefficient and expensive one.
Aldehydes can be prepared by various techniques, for example, by hydroformylation. However, aldehydes produced by such method normally appear as mixtures of straight chain and branch chain aldehydes. In this connection, it is many times difficult to provide a relatively pure linear aldehyde product if that is desired. Moreover, the question always remains as to what to do with the undesired branched aldehyde by-product. An alternative use for the branched product can be found, it can be converted into some other desired product, or it can be converted into a material which is used then in some other process or is even discarded.
It would be highly desireable to provide a process which facilitates the separation of straight and branched chain aldehydes, especially of para-t-butyl phenylpropionaldehyde and para-t-butyl-alpha methylphenylacetaldehyde. Moreover, it would be very advantageous if the process produced a product which has a commercial utility in itself or is usable as a starting material and in the overall process to obtain the desired product.
Various references have disclosed decarbonylation employing palladium as a catalyst. See, for example, Newman et al., "The Catalytic Dehydrogenation Of 2-Substituted--5, 6, 7, 8-Tetrahydronaphthalene Derivitives" J.A.C.S., Vol. 65, pp. 1097-1101 (1943); Newman et al., "A New Method of Introducing The Neopentyl Group" J. Org. Chem. Vol. 31, pp. 3860 et seq. (1966); Hawthorne et al., "Decarbonylation Of Aromatic Aldehydes" J. Org. Chem., Vol. 25, pp. 2215-2216 (1960); Chemical Abstracts, Vol. 75, Abstract No. 140422 (1971). However, to our knowledge, no one has suggested that such a palladium catalyst could be employed in a selective decarbonylation of branched aldehyde (especially para-t-butyl-phenylpropionaldehyde) from a mixture also containing a linear aldehyde (e.g., para-t-butyl-alphamethyl-phenylacetaldehyde), for example, from the reaction product mixture of a hydroformylation reaction.